You're correct. I should have specified that the values do not matter. I have updated the README to account for this. The reason why I wanted to make this an op

You're correct. I should have specified that the values do not matter. I have updated the README to account for this. The reason why I wanted to make this an option is because, in certain cases, someone may want to keep their headers as a collection of ids pointing to something else, and I wanted to allow them to be able to just pass in this collection/object literal without having to convert it to an array.